1. Field of the Invention
The present invention relates to a process and to a device for the production of a single crystal of semiconductor material by pulling the single crystal from a melt, which is contained in a crucible and is heated by a side heater surrounding the crucible.
2. The Prior Art
This process for producing single crystals is referred to as the Czochralski method. It is already known that the incidence of specific types of defects in single crystals which are grown depends on the pull rate V and the axial temperature gradient G at the phase boundary between the single crystal and the melt. If the conditions during the pulling of the single crystal are such that the condition V/G&lt;C.sub.crit is satisfied, C.sub.crit being a constant, then a majority of interstitial defects, known as large pits, are formed (E. Dornberger, W. v. Ammon in Electrochemical Society, Vol. 143, No. 5 (1996)). This type of defect, referred to below as L-defects, can greatly reduce the yield of functional electronic components which are produced by further processing the single crystal. The condition indicated above makes it clear that, in order to avoid the occurrence of L defects, attempts should be made to keep the pull rates as high as possible.
However, when pulling a single crystal, it is found that the pull rate can only be increased up to a certain degree without unacceptably altering the way in which the single crystal grows. Specifically, at excessive growth rates, the single crystal starts to lose the desired cylindrical growth and starts to grow in an imperfectly round shape. Thus instead of forming a cylindrical lateral surface, the single crystal starts to form plane crystal faces corresponding to its crystallographic orientation. Further, growth which is not perfectly round increases the risk of producing crystal lattice defects in the pulled material which renders it unusable.